Re: [ATM] undercorrecting?

[Nils Olof Carlin <nilsolof.carlin@telia.com>]

>If the mirror is truly equalized, how can the front surface be at a 
different temperature than ambient?  Then it is not equalized.

Equalized is perhaps an unfortunate term. But at equilibrium, this may 
well be the case - In the sun, at equilibrium, the top side of a car is 
warmer than the underside ;-)

Now if the mirror were "black" in the relevant IR wavelength (I 
believe of the order of 10 micron wavelength) at the side turned to the 
sky, it could cool by radiation loss. I suspect it is rather reflective 
here and this cooling wouldn't be very efficient, but I don't know. If 
the sky, seen from the mirror, takes only a minimum steric angle such 
as from a bottom of a tube (solid or shrouded), radiative cooling would 
be small and possibly negligible. If you ever get dew on your primary, 
it isn't, of course.

Nils Olof


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